The entrance to a large lecture room consists of two side-by-side doors, one hinged on the left and the other hinged on the right. Each door is 0.680 m wide. Sound of frequency 646 Hz is coming through the entrance from within the room. Take the speed of sound to be 345 m/s. What is the diffraction angle of the sound after it passes during the doorway when (a) one door is open and (b) both doors are open?